This function is
EXPERIMENTAL. The behaviour of this function, the
name of this function, and anything else documented about this
function may change without notice in a future release of PHP.
Use this function at your own risk.
Get the property name used to refer to this data object
by its containing data object.
Parameters
None.
Return Values
Returns the name of the container's property which references
this SDO_DataObject,
or returns NULL if this is a root SDO_DataObject
(i.e. it has no container).
